Abundance
Calcium carbonate is naturally abundant in the forms of the mineral calcite, the sedimentary rock limestone, and chalk deposits.
Calcite:
This mineral is very common; it makes up 4% of the weight of the earth’s crust, that is, it is a material in the many kinds of rocks that make up the earth’s crust like limestone and marble (which is limestone morphed by heat and pressure). Calcite is also found in a more rare type of igneous rock called carbonatite, a rock which plays a role in volcanic eruptions and is found near fault lines.
In its pure form calcite is the calcium carbonate crystal (see structure page). It comes in many different colors and has many different uses because of its natural occurrence in many different areas. For example Mexican onyx which is multi-colored and used for aesthetic purposed while Iceland spar is almost colorless and is used for its optical properties (see uses page).
Calcite makes up part of many sea organisms’ outer protective shells such as coral algae, diatoms, and shell fish.
Chalk:
Calcium carbonate is tied to the ocean in another way, when the smaller organisms with calcite shells die the calcium carbonate turns to a white powdery form of chalk. Chalk deposits are in oceans and on land where ocean once were. The on land chalk deposits are only one of the natural sources of calcite, but they are the easiest to obtain and work with since it is in particles, a powdery like form.
Limestone:
Limestone is also made of small fragments of larger animal shells, and the study of these fossils is important to leaning about the history of the earth (see uses page). Limestone often contains dolomite as well as calcite. Limestone is an abundant sedimentary rock formed by the calcite shells after those bodies of water have evaporated. Limestone is abundant, and is seen in most canyons, gorges and waterfalls, because of the depth at which and way they are formed.
Calcium carbonate is obtained from limestone, marble, and chalk deposits all over the earth. To be commercially used it is ground into a powder. Here is a picture of a truck at the source of calcium carbonate and of a plant where calcium carbonate is produced:
Pictures’ Resource: http://us.geocities.com/hayayoo/work.htm